Risk factors for dislocation after revision total hip arthroplasty with a dual-mobility cup. Matched case-control study (16 cases vs. 48 controls).

BACKGROUND: Reports of high dislocation rates after revision total hip arthroplasty (THA) have encouraged the widespread use of dual-mobility cups. Dislocation has been less common but not fully abolished with dual-mobility cups, and its causes have remained unidentified. The objectives of this retrospective matched case-control study were: 1) to identify risk factors for dislocation, 2) and to assess dislocation outcomes. HYPOTHESIS: The causes of dislocation after revision THA with a dual-mobility cup can be identified. MATERIAL AND METHOD: Among 653 consecutive patients identified retrospectively as having undergone revision THA with a dual-mobility cup (Medial Cup, Aston, Saint-Étienne, France) between January 2007 and December 2017, 16 (2.45%) subsequently experienced dislocation, after a mean of 3.6 months (range, 0.9-19 months). For each of these 16 patients, we collected the main patient characteristics (age, sex, body mass index [BMI], ASA score, and reason for the initial arthroplasty procedure), local history (number of previous surgical procedures, reason for revision, femoral and acetabular bony defects classified according to Paprosky, and status of the abductor apparatus), and characteristics of the revision (approach, diameters of the cup and femoral head, cup inclination, femoral offset, lower limb length, and implant anteversion). Controls were patients without dislocation after revision dual-mobility THA. Each of the 16 patients was matched to 3 controls on age (±10 years), sex, year of revision, and whether revision was only acetabular or bipolar. Univariate and multivariate analyses were done to compare the cases and controls, and dislocation outcomes in the cases were evaluated. RESULTS: By univariate analyses, factors associated with dislocation were BMI>30 (cases, 37.5%; controls, 10.4%; p=0.02), larger number of previous surgical procedures on the same hip (cases, 2.8; controls, 1.8; p=0.004), larger number of arthroplasties (cases, 2.3; controls, 1.5; p=0.004), history of instability (cases, 31% with chronic dislocation and 13% with recurrent dislocation; controls, 6.25% and 2.1%, respectively; p=0.004), and compromised abductor apparatus (cases, 56.25%; controls, 14.6%; p=0.002). Independent risk factors for dislocation identified by multivariate analysis were instability (odds ratio [OR], 14.5; 95% confidence interval [95%CI], 1.5-149.9) and, most importantly, abductor apparatus compromise (OR, 43.1; 95%CI, 3.18-586.3). Of the 16 cases, 1 was lost to follow-up, 1 had contra-indications to anaesthesia, 1 died after several dislocation episodes, and 1 died 3 months after surgical reduction. In 5 cases, there was a single dislocation episode. Further surgery was performed in 8 cases (surgical reduction, n=1; constrained cup, n=3; trochanteric internal fixation, n=1; exchange of the dual-mobility cup, n=2, including 1 with subsequent dislocation episodes; and femoral component exchange followed by a retentive cup due to further dislocation episodes, n=1). CONCLUSION: Risk factors for dislocation consisted of a history of instability and, most importantly, abductor apparatus compromise. A constrained cup should be considererd in patients with impaired abductor apparatus. No further dislocations occurred after reduction of the first episode in 31.25% of cases. Recurrent dislocation should prompt measures to correct impaired abductor apparatus whenever possible, as well as correction of any component malposition. Whether a retentive cup should be implanted routinely remains unclear. LEVEL OF EVIDENCE: III, matched case-control study.

Are spinoglenoid ganglion cysts early markers of glenohumeral arthritis?

HYPOTHESIS: The objective of this study was to improve our understanding of the pathogenesis and symptoms of ganglion cysts (GCs) in the spinoglenoid notch. Two hypotheses were tested: (1) the labral tears responsible for these cysts are mainly degenerative and nontraumatic, (2) spinoglenoid cysts are early magnetic resonance image (MRI) markers of eccentric posterior glenoid wear. MATERIALS AND METHODS: This was a descriptive diagnostic study. Patients were included when a spinoglenoid cyst was discovered after complaints of pain in the posterosuperior aspect of the shoulder. MRI and arthroscopy were used to classify the glenoid GC and characterize the glenohumeral joint. The GCs were classified into 1 of 3 types: GC0 (isolated cyst), GC1 (cyst and associated labral lesion), and GC2 (cyst and associated labral and cartilage lesion). RESULTS: Twenty patients (average age, 43 years) were included between 2000 and 2014. There were 7 GC0, 8 GC1, and 5 GC2 type cysts. Isolated labral tears (GC1) were always located posteriorly, without anterior extension or glenoid detachment. The humeral subluxation index was above 55% in 75% of shoulders, including all of the type GC2 shoulders. The 5 GC2 shoulders had type B1, B2, or C glenoids. CONCLUSIONS: The management of paraglenoid labral cysts must go beyond addressing the suprascapular nerve compression related to traumatic labral detachment, and surgeons should look automatically for associated degenerative joint damage. The diagnosis of GCs should be supplemented by humeral subluxation index measurement on computed tomography scan or MRI, and the patient should be informed that joint-related posterior shoulder pain might persist in cases of GC1 and GC2. LEVEL OF EVIDENCE: Basic Science Study; Anatomy; Imaging and In Vivo.